LM4810

SNAS125D – FEBRUARY 2001 – REVISED APRIL 2013

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POWER SUPPLY BYPASSING

As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply

rejection. Applications that employ a 5V regulator typically use a 10µF in parallel with a 0.1µF filter capacitors to

stabilize the regulator's output, reduce noise on the supply line, and improve the supply's transient response.

However, their presence does not eliminate the need for a local 1.0µF tantalum bypass capacitance connected

between the LM4810's supply pins and ground. Keep the length of leads and traces that connect capacitors

between the BYPASS pin and ground improves the internal bias voltage's stability and improves the amplifier's

PSRR. The PSRR improvements increase as the bypass pin capacitor value increases. Too large, however,

desired PSRR requirements, click and pop performance (as explained in SELECTING PROPER EXTERNAL

COMPONENTS), system cost, and size constraints.

SELECTING PROPER EXTERNAL COMPONENTS

Optimizing the LM4810's performance requires properly selecting external components. Though the LM4810

operates well when using external components with wide tolerances, best performance is achieved by optimizing

component values.

The LM4810 is unity-gain stable, giving a designer maximum design flexibility. The gain should be set to no more

than a given application requires. This allows the amplifier to achieve minimum THD+N and maximum signal-to-

noise ratio. These parameters are compromised as the closed-loop gain increases. However, low gain demands

input signals with greater voltage swings to achieve maximum output power. Fortunately, many signal sources

for more information on selecting the proper gain.

Input and Output Capacitor Value Selection

Figure 1). A high value capacitor can be expensive and may compromise space efficiency in portable designs. In

many cases, however, the speakers used in portable systems, whether internal or external, have little ability to

reproduce signals below 150Hz. Applications using speakers with this limited frequency response reap little

improvement by using high value input and output capacitors.

magnitude of the pop is directly proportional to the input capacitor's size. Thus, pops can be minimized by

selecting an input capacitor value that is no higher than necessary to meet the desired

−3dB frequency. Please

refer to the OPTIMIZING CLICK AND POP REDUCTION PERFORMANCE for a more detailed discussion on

click and pop performance.

-3db high pass filter cutoff frequency defined by Equation 4.

(3)

(4)

Also, careful consideration must be taken in selecting a certain type of capacitor to be used in the system.

Different types of capacitors (tantalum, electrolytic, ceramic) have unique performance characteristics and may

affect overall system performance.

Bypass Capacitor Value Selection

value is critical when minimizing turn-on pops. The slower the LM4810's outputs ramp to their quiescent DC

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